Field of the Invention
The invention relates to a method of controlling the quantity of ink located in an inking unit of a printing machine during the processing of a print job. The greater this ink quantity, the more intensive is the inking of the ink-accepting areas of a printing plate; the smaller the ink quantity, the less intense is the inking. It is therefore important to keep this quantity of ink constant, as long as the printing result is satisfactory in terms of inking and, if deviations in terms of inking are established, to be able to set the quantity of ink as quickly as possible to a new value, due to which it is expected that a printed result which is satisfactory in terms of inking will be delivered.
The inking unit of a printing machine is usually supplied with ink from an ink source, for example, in the form of an ink fountain with a metering device. It includes a more-or-less large number of inking rollers, which feed the flow of ink metered by the ink source to the printing plate. In order to set the quantity of ink in the inking unit or on an inking roller to a different value, it is necessary to vary the flow of ink released from the ink source. Because this flow of ink is distributed to a large number of rollers before it reaches the printing plate, some time elapses between the detection of a deviation in the inking and a corresponding resetting of the metering device, on the one hand, and the time at which the changed metering has any effect upon the ink supply of the printing plate, on the other hand. During this time period, rejects or waste are produced.
It is of great interest to keep the time period as short as possible. For this purpose, a method has been developed wherein an increase or reduction in the quantity of ink on the roller from a first to a second value is produced in that, during a transition time period, a flow of a quantity of ink is released which is, respectively, above and below a desired or nominal value of the ink quantity flow, corresponding to the second value, and which is defined in accordance with a given rule as a function of the first and the second quantity of ink. If the second quantity of ink is greater than the first, the flow of ink quantity in the transition time period is greater than the flow of ink quantity corresponding to the second quantity of ink; if the second quantity of ink is smaller than the first, the flow of ink quantity in the transition time period is smaller. This means that, for a period of time, an excess of ink or too little ink is fed from the ink source, in order to arrive as quickly as possible at the desired quantity of ink on the inking roller and, after the expiration of a time period, following which this second quantity of ink should approximately have been reached, a change is made to the second flow of ink quantity, which is dimensioned so that the second quantity of ink on the roller is maintained during continuous operation.
A corresponding method is also described in the published German Patent Document DE 43 37 343 A1.
It is an object of the invention to provide a method of controlling a quantity of ink in a printing machine which avoids the foregoing disadvantages of the heretofore known methods of this general type and is an improvement over the conventional methods.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a method of controlling a quantity of ink in an inking unit of a printing machine, which includes maintaining a constant quantity of ink in the inking unit by releasing an appropriate, constant flow of ink quantity from an ink source, and producing an increase and a decrease, respectively, of the quantity of ink from a first value to a second value by releasing, during a transition time period, a flow of ink quantity lying, respectively, above and below a second nominal value of the flow of ink quantity, corresponding to the second value, and which is defined in accordance with a given rule as a function of the first and the second quantity of ink, which comprises setting the quantity of ink to a third value during the transition time period from the first to the second value of the quantity of ink, interpolating an imaginary quantity of ink between the first and the second quantity of ink, beginning a new transition time period, and defining the flow of ink during the new transition time period, using the given rule as a function of the imaginary quantity of ink and the third quantity of ink.
In accordance with another mode, the method includes keeping the flow of ink quantity constant during the transition time period.
In accordance with a further mode, the method includes maintaining an integral over a transition time period of a difference between the flow of ink quantity released during the transition time period and the flow of ink quantity to be released after the transition time period, proportional to the difference between the quantities of ink before and after the transition.
In accordance with a concomitant mode, the method includes interpolating the imaginary quantity of ink as follows:       F    f    =            F      1        +                                                      ∫                              t                1                                            t                3                                      ⁢                          s              ⁡                              (                t                )                                              -                                    s              2                        ⁢                          ⅆ              t                                                                          ∫                              t                1                                            t                2                                      ⁢                          s              ⁡                              (                t                )                                              -                                    s              2                        ⁢                          ⅆ              t                                          ⁢                        (                                    F              2                        -            F                    )                1            
wherein t3 is the time at which the third nominal value is predefined, and s(t) is the flow of ink quantity released in the transition time period.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as a method for controlling a quantity of ink in a printing machine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific modes when read in connection with the accompanying drawings, wherein: